Information handling system utilizing circuitized substrate

ABSTRACT

An information handling system (e.g., computer, server, etc.) Utilizing at least one circuitized substrate assembly of robust construction and possessing enhanced operational capabilities. The substrate assemblies include a substrate having at least one opening which is substantially filled with a conductive paste prior to bonding. Once bonded, the paste is also partially located within the other opening to provide an effective electrical connection therewith.

CROSS-REFERENCE TO CO-PENDING APPLICATIONS

This application is a divisional application Ser. No. 10/379,575,entitled “Information Handling System Utilizing Circuitized Substrate”and filed Mar. 6, 2003 (inventors: J. W. Fuller et al), which in turn isa continuation-in-part of application Ser. No. 10/322,527, filed Dec.19, 2002 now U.S. Pat. No. 6,809,269, and entitled: “CircuitizedSubstrate Assembly and Method of Making Same”. The inventors of thiscontinuation-in-part are also J. W. Fuller et al.

TECHNICAL FIELD

The present invention relates information handling systems andparticularly those which use circuitized strictures such as printedcircuit boards (PCBs).

BACKGROUND OF THE INVENTION

By the term “information handling system” as used herein shall mean anyinstrumentality or aggregate of instrumentalities primarily designed tocompute, classify, process, transmit, receive, retrieve, originate,switch, store, display, manifest, measure, detect, record, reproduce,handle or utilize any form of information, intelligence or data forbusiness, scientific, control or other purposes. Examples includepersonal computers and larger processors such as servers, mainframes,etc. Such systems typically include one or more PCBs as integral partsthereof, each PCB including a plurality of various components such ascapacitors, resistors, modules, etc. mounted thereon. One such PCB canbe referred to as a “motherboard” while various other boards (or cards)may be mounted thereon using suitable electrical connectors.

One method of forming a laminate circuitized board structure for use insuch information handling systems includes forming layers of dielectricmaterial and electrically conducting material to provide multiple layersof circuits and voltage planes. Circuits can be discrete wiring patternsknown as signal planes. Voltage planes can be either ground plane orpower planes, and are sometimes collectively referred to as powerplanes. In one technique of forming such structures, layers ofdielectric material and conductive material are successively applied,i.e., the dielectric material is applied and then circuits or voltageplanes are provided thereon and, if necessary, through holes formed bydrilling or etching. This method relies on each successive step ofadding additional structure and the circuitry layers are formedindividually, e.g., in each step in forming the plane having circuittraces or formed power planes. This requires precision drilling to formthe plated through holes (PTHs) all of which is time consuming,especially where there is a large number of drilled holes required toform PTHs.

More recently, methods have been described that provide a relativelyinexpensive photolithographic technique of forming a composite laminatestructure (substrate assembly) from individual discrete laminatestructures (substrates). For example, see U.S. application Ser. No.09/812,261, entitled “Printed Wiring Board Structure With Z-AxisInterconnections” and filed Mar. 19, 2001. See also U.S. Pat. No.6,388,204 (Lauffer et al) and U.S. Pat. No. 6,479,093 (Lauffer et al),the teachings of which are incorporated herein by reference. Althoughthe structures and methods of these inventions provide significantadvances and advantages over current PCB fabrication methods, therestill exists a need for further refinement. Therefore, continuingefforts are underway in attempting to provide for even greateradvantages. The invention defined in parent application Ser. No.10/322,527 represents one excellent example of a new circuitizedsubstrate specifically adapted for use in information handling systemssuch as described above.

It is believed that such an improved system will constitute asignificant advancement in the art.

OBJECTS AND SUMMARY OF THE INVENTION

It is a primary object of the present invention to enhance theinformation handling system art.

According to one aspect of the invention, there is provided aninformation handling system comprising a circuitized substrate assemblyincluding a first circuitized substrate including an opening therein, asecond circuitized substrate bonded to the first circuitized substrateand including an opening therein substantially aligned with the openingin the first circuitized substrate, and a quantity of electricallyconductive paste substantially completely filling the opening in thesecond, bonded circuitized substrate and only partly filling the openingin the first circuitized substrate.

According to yet another aspect of the invention, there is provided aninformation handling system comprising a circuitized substrate assemblyincluding a first circuitized substrate including an opening therein, asecond circuitized substrate bonded to the first circuitized substrateand including an opening therein aligned with the opening in the firstcircuitized substrate, an electrically conductive cover membersubstantially covering the opening in the second circuitized substrateon the surface of the second circuitized substrate facing the firstcircuitized substrate, and a quantity of electrically conductive pastepositioned on the cover member and only partly filling the opening inthe first circuitized substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side-elevational view of a circuitized substrate assembly(prior to bonding thereof) capable of being used in an informationhandling system, according to one embodiment of the invention;

FIG. 2 is a side-elevational view of the assembly of FIG. 1 followingbonding;

FIG. 3 is a side-elevational view of an alternative embodiment of acircuitized substrate assembly for use in the present invention;

FIG. 4 is a side-elevational view of the assembly of FIG. 3 followingbonding; and

FIG. 5 is a perspective view of one example of an information handlingsystem that can utilize one or more of the circuitized substrates formedaccording to the teachings herein.

BEST MODE FOR CARRYING OUT THE INVENTION

For a better understanding of the present invention, together with otherand further objects, advantages and capabilities thereof, reference ismade to the following disclosure and appended claims in connection withthe above-described drawings. It is understood that like numerals willbe used to indicate like elements from FIG. to FIG.

The following terms will be used herein and are understood to have themeanings associated therewith. By the term “circuitized substrate” ismeant to include substrates including at least one dielectric layer andone conductive layer therein or thereon. Examples include printedcircuit boards or like structures made of dielectric materials such asfiberglass-reinforced epoxy resins, polytetrafluoroethylene (Teflon),polyimides, polyamides, cyanate resins, photoimageable materials,ceramic and other like materials wherein the conductive layer is a metallayer (e.g., power or signal plane) comprised typically of copper butmay include or comprise additional metals (e.g., nickel, aluminum, etc.)or alloys thereof. If the dielectric is a photoimageable material, it isphotoimaged or photopatterned, and developed to reveal the desiredcircuit pattern, including the desired opening(s) as defined herein, ifrequired. The dielectric material may be curtain coated or screenapplied, or it may be supplied as the dry film. Final cure of thephotoimageable material provides a toughened base of dielectric on whichthe desired electrical circuitry is formed. An example of a specificphotoimageable dielectric composition includes a solids content of fromabout 86.5 to about 89%, such solids comprising: about 27.44% PKHC, aphenoxy resin; 41.16% of Epirez 5183, a tetrabromobisphenol A; 22.88% ofEpirez SU-8, an octafunctional epoxy bisphenol A formaldehyde novolacresin; 4.85% UVE 1014 photoinitiator; 0.07% ethylviolet dye; 0.03% FC430, a fluorinated polyether nonionic surfactant from 3M Company; 3.85%Aerosil 380, an amorphous silicon dioxide from Degussa to provide thesolid content. A solvent is present from about 11 to about 13.5% of thetotal photoimageable dielectric composition. The dielectric layerstaught herein may be typically about 2 mils to about 4 mils thick.

By the term “circuitized substrate assembly” as used herein is meant toinclude at least two of such circuitized substrates in a bondedconfiguration, one example of bonding being conventional laminationprocedures known in the art.

By the term “electrically conductive paste” as used herein is meant toinclude a bondable (e.g., capable of lamination) conductive materialcapable of being dispensed within openings of the type taught herein.Typical examples of bondable electrically conductive material areconductive pastes such as silver filled epoxy paste obtained from E. I.duPont deNemours under the trade designation CB-100, Ablebond 8175 fromthe Ablestick Company and filled polymeric systems, thermoset orthermoplastic type, containing transient liquid conductive particles orother metal particles such as gold, tin, palladium, copper, alloys, andcombinations thereof. One particular example is coated copper paste.Metal coated polymeric particles disposed in a polymeric matrix can alsobe used.

Finally, by the term “sticker sheet” as used herein is meant to includedielectric materials such as conventional pre-preg materials used inconventional, multilayered PCB construction, e.g., usually bylamination. Other examples include the products Pyrolux and liquidcrystal polymer (LCP) or other freestanding films. These dielectricsticker sheets may be adhesively applied to one or both of the twocircuitized substrates to assist in bonding these two components. Thesesheets may also be patterned, e.g., by laser or photoimaging, ifdesired. Significantly, such sheets can also include a conductive plane(including signal, ground and/or power) therein to further increase thecircuit density of the finished, bonded product taught herein. Suchsticker sheets may be typically 5 to 8 mils (thousandths) thick.

In FIG. 1 there is shown a circuitized substrate assembly 10 which, whenfinally formed (FIG. 2), can be used in an information handling system,such as a computer server 12 shown in FIG. 5. Assembly 10 includes firstand second circuitized substrates 11 and 13, and may further includeadditional circuitized substrates such as substrate 15. In one example,a total of from two to twenty circuitized substrates may be utilized toform a final circuitized substrate assembly. First substrate 11 includesa plurality of layers of dielectric material 17 as described above withalternating layers of conductive material 19 therein. As stated, suchconductive layers may include signal, ground or power planes of the typetypically found in many PCB constructions. Such conductive layers 19 arealso patterned in accordance with the operational requirements for thefinished assembly to be used in system 12. The cross-sectionalconfigurations depicted in these drawings are thus representative only.In one example, a total of eight dielectric layers and seven conductivelayers may be utilized to form each substrate 11. The seven conductivelayers of this example may include four signal layers and three powerplanes.

First substrate 11 includes an opening 21 therein. Opening 21 extendsthrough the entire thickness of the first substrate 11. In FIG. 1,opening 21 further includes a conductive (e.g., copper) plating 23 whichextends along the internal walls of opening 21 and outwardly onto theexternal opposing surfaces of substrate 11. These external portions oflayer 23 may be referred to as lands, pads or the like for eventualelectrical connection to another conductive member (in the case ofsubstrate 13, to other lands). Opening 21 preferably includes a diameterof from about 1 to about 15 mils. The remaining openings describedherein also each preferably include a similar diameter.

Second substrate 13 is similar to first substrate 11, including havingdielectric layers 17 and conductive layers 19 as part thereof. Secondsubstrate 13 also includes an opening 21 similar to that in substrate11. Further, substrate 13 includes a conductive layer 23 similar also tothat of layer 23 in FIG. 1. Layer 23 may also include the external lands(or pads) of the type shown for substrate 11. In one example, bothconductive layers 23, and the external lands may possess a thickness offrom about 0.5 mils to about 3.0 mils.

Significantly, opening 21 in second substrate 13 further includes aquantity of electrically conductive paste 25 therein. As seen in FIG. 1,paste 25, of the type defined in detail above, completely fills opening21 in the second substrate. Additionally, the electrically conductivepaste 25 may also extend outwardly onto the external surfaces of thelands of layer 23 as also shown in FIG. 1. In one example, a total of400 cubic mils of paste may be applied to each external land on bothsurfaces of the second substrate. Paste application can be performed byconventional techniques such as stencil printing, screen printing orinjection. Further description is thus not believed necessary.

Only two circuitized substrates may be utilized to perform a final,bonded assembly 10. As shown in FIG. 1, however, the utilization of athird circuitized substrate 15 will also be described. Substrate 15 isthus substantially similar in components as substrates 11 and 13. It isalso to be noted that although the patterns of dielectric and conductivelayers within the various substrates shown are similar, the invention isnot limited to these configurations. Several different patterns oflayers can be utilized for the various substrates.

With the substrates aligned in the orientation shown in FIG. 1, the nextstep is to bond the substrates to form assembly 10. Such a bondedassembly 10 is shown in FIG. 2. The preferred method of accomplishingsuch bonding is to use a conventional laminating process, which, in oneexample, is carried out at temperatures from about 70 to about 200degrees Celsius (C.) for a time period of about 30 to about 180 minutesand under a laminating pressure of from about 50 to about 500 pounds persquare inch (p.s.i.).

In a preferred embodiment, a sticker sheet 31 is positioned between therespective substrates prior to lamination for the purpose of improvingthe bond between the substrates. The preferred sticker sheet material isdefined hereinabove. It is understood that use of such a sticker sheetis not essential to achieve a satisfactory bond between the circuitizedsubstrates taught herein. As clearly seen in FIG. 1, the dielectricsticker sheet 31 does not physically engage conductive paste 25 prior tothe bonding of the substrates. It cannot, therefore, provide support forthe paste during the bonding steps.

In FIG. 2, the bonded circuitized substrate assembly 10 is fullycompressed as a result of the aforedefined lamination process.Significantly, the conductive paste 25 has extended from its originalposition both upwardly and downwardly to partially fill the respectiveopposing openings 21 in substrates 11 and 15. Of further significance,paste 25 also extends between the opposing faces of the respective landsof layers 23 formed on the external surfaces of the respectivesubstrates. Thus, an effective electrical connection has been attainedbetween the conductive layers 23 of all three substrates using but asingular quantity of conductive paste 25. Such interim placement ofconductive paste 25 between the lands further enhances the electricalconnection between the respective substrates in the manner taughtherein.

Additional operations may now be performed on the bonded assembly 10,including the addition of another dielectric layer 33 and a conductiveland 35 or the like which extends downwardly to contact the exposed landportion of a respective land portion of layer 23. Layer 33 may serve asa mounting layer or the like for additional electrical components (notshown) which may be positioned thereon.

In FIG. 3 there is shown a bonded circuitized substrate assembly 10′which can also be used in the present invention. Assembly 10′ includesthe same components as shown in the embodiment of FIG. 1 with theexception that conductive paste is not filled within the opening 21 ofsubstrate 13. Instead, a cover member 41 is provided over the externalland portions of layer 23 of substrate 13. A preferred cover member is ametallic layer, e.g., copper. Prior to positioning of cover member 41,the opening in substrate 13 is preferably filled with a dielectric orother material (including conductive) 43. In a preferred embodiment,material 43 is a dielectric material of the type described above. Withsuch dielectric material in place, cover members 41 may be plated overthe external exposed surfaces of the positioned dielectric 43. In oneexample, cover layer 41 may include a thickness of from about 0.1 milsto about 2.0 mils.

As further seen in FIG. 3, a quantity of conductive paste 25 ispositioned over the cover member 41 and is comprised of a similar pasteas used in the embodiment of FIG. 1. In one example, a quantity of 400cubic mils of paste 25 is applied onto cover member 41 and will possessa thickness of only about 2 mils. In FIG. 3, two quantities of paste areutilized, but it is again understood that only two substrates (11 and13) may be utilized to form a successfully bonded final structure 10′.

In FIG. 4, the exploded structure 10′ in FIG. 3 is shown as beingbonded, preferably using a lamination process as described above.Significantly, the respective quantities of paste 25 have extendedoutwardly from the cover member 41 to partially fill the opening in therespective opposing substrate. Of further significance, a portion of theconductive paste 25 remains positioned between the external surfaces ofthe outwardly projecting land portions of the respective layers 23 toeven further enhance the electrical coupling between the respectivesubstrates. As in the embodiment of FIG. 1, a dielectric 33′, inaddition to an external conductor 35′, may also be added, including onopposite sides of the formed assembly 10′.

The substrates produced herein are of a robust structure, in turnassuring a more robust final system using same. One reason is thatcomplete initial filling of all substrate openings with paste prior tofinal joining is not necessary, which filling would require moreexacting process tolerances to achieve high joining yield and reliablestructures. For example, such fillings would require the thickness ofthe 2 conductive pads to be joined plus the thickness of the conductiveadhesive to be roughly equal to the sticker sheet. If the sticker sheetis thicker, then there could be poor contact of the conductive joints.If the pads plus paste are thicker than the sticker sheet, then therecould be voids in the sticker sheet, or the conductive paste could besqueezed laterally, to the extent of possibly shorting adjacent pads.For such requirements, tolerance requirements were less than 1 mil,while the sum of the tolerance capabilities was significantly higherthan 1 mil. The substrates made according to the methods taught hereinovercome these problems, to thus assure a final system of higherquality. Information handling systems, including one or more circuitizedsubstrates as taught herein, are able to provide significant operationalcapabilities over systems utilizing conventional printed circuit boardconstructions. This is primarily due to the increased wiring densitiesand that wiring PTHs are no longer needed to go through the system'ssubstrates. Resulting systems can also be provided at lower cost due tothe corresponding reduced cost of the substrates used therein.

The information handling systems utilizing the substrates taught hereinthus represent significant advancements in the art.

While there have been shown and described what are at present thepreferred embodiments of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the scope of the invention as defined bythe appended claims.

1. An information handling system comprising a circuitized substrateassembly including a first circuitized substrate including an openingtherein, a second circuitized substrate bonded to said first circuitizedsubstrate and including an opening therein aligned with said opening insaid first circuitized substrate, an electrically conductive covermember substantially covering said opening in said second circuitizedsubstrate on the surface of said second circuitized substrate facingsaid first circuitized substrate, and a quantity of electricallyconductive paste positioned on said cover member and only partly fillingsaid opening in said first circuitized substrate.
 2. The informationhandling system of claim 1 wherein said first and second circuitizedsubstrates each include at least one electrically conductive plane andat least one dielectric layer.
 3. The information handling system ofclaim 1 wherein each of said openings in said first and secondcircuitized substrates includes an electrically conductive materialthereon, said electrically conductive paste being in electrical contactwith said electrically conductive material in said opening in said firstcircuitized substrate.
 4. The information handling system of claim 3wherein said electrically conductive material comprises a plated layerof metal.
 5. The information handling system of claim 1 furtherincluding an interim dielectric layer between said first and secondcircuitized substrates.
 6. The information handling system of claim 1further including a layer of dielectric material positioned on anexternal surface of said first circuitized substrate and extendingwithin said opening of said first circuitized substrate.
 7. Theinformation handling system of claim 1 wherein said cover membercomprises a metallic layer.
 8. The information handling system of claim7 wherein said metallic layer is copper.
 9. The information handlingsystem of claim 1 wherein said opening in said second circuitizedsubstrate is filled with a dielectric material, said cover member beingpositioned on said dielectric material.
 10. The information handlingsystem of claim 1 further including a third circuitized substrate alsohaving an opening therein and bonded to said second circuitizedsubstrate such that said opening in said third circuitized substrate issubstantially aligned with said opening in said second circuitizedsubstrate, said assembly further including a second cover membersubstantially covering said opening in said second circuitized substrateand a second quantity of electrically conductive paste positioned onsaid second cover member and only partly filling said opening in saidthird circuitized substrate.
 11. The invention of claim 1 wherein saidinformation handling system comprises a computer or a server.